Are renewables not a relatively expensive way to lower carbon emissions?

If you want to compare apples and oranges, yes.

It is often claimed, for instance, that insulation is a much cheaper way. But even if we insulate our homes better, we still have to decide how we are going to make electricity.

But although renewables have been expensive in the past, they are increasingly becoming the cheapest option. New renewables are now much cheaper than building a new nuclear plant, and all estimates going forward are that renewables will be the least expensive source of low-carbon electricity in Germany within this decade. These prices are for new plants, not decades-old central power stations that have already been completely written down.